Man7:
Why can't you debate this subject without making smart-arse patronising remarks.
Have you actually ever got your feet wet in the mud of numerous UK estuaries and bays ?? I have, as recently as this afternoon in fact.
Because while your other comments were sensible and worthwhile, that particular one was pretty inane. We were talking about building on sand, and then you talk about alluvial muds - is that a sensible contribution to the debate?
Actually, I used to be in mineral surveying, so i know a little about this. And I don't even know why we are debating this subject, because building on land reclaimed with sand is a known technique. it has been used for over 500 years, and is still being used to this day.
This is Dutch land reclamation today - using clean sand and not alluvial muds:
And this is the Palm Resort similarly being reclaimed from the sea with sand:
In other words this technique is a known factor, and it works. Although the Palm Resort's idea of leaving the sand 'uncontained' (because it looks nicer) is stretching the technique to its limits. As I said before, the sand needs to be stabilised and contained (preferably within a concrete wall). As anyone who has built a sand-castle will know, if you leave sand unbounded and uncontained it - well - disperses quite rapidly.
Jabird:
Now I don't have a Thames Estuary contour map to hand, but I put it to you that your island would be several times deeper than Foster's only partially offshore proposal at its deepest point.
Now that is a better question. Maplin sands (north coast) is about 1 fathom over a large area, and Margate sands (south shore) is about 2 fathoms over an even wider area. I may have Silver Island too far north, and thus dropping the northerly two runways into the main channel, which would not be a good idea - in which case the island may need to drift south a little, or put the domestic runways on the south side.
Yes, the Silver-Foster proposal on the Isle of Grain has little or no reclamation required, it is true. But you have still not proposed how you overcome the Greens and their endangered fibonacci snail. How do you deal with tented encampments sitting there for decades? Lampposts and ropes might do the trick, but that is not very PC.
And is the noise factor for local communities in Gravesend and Chatham acceptable or not? (Although the extra jobs for these fairly run-down communities might be a big bribe.)
Jabird:
There is also the question of how the various Thames ports would operate if Silver barrage was closed? Locks in such a structure would be prohibitively expensive.
Lock provision is a consequence of the barrage, not Silver Island. But since London will need a larger barrage anyway it just makes more sense to combine the two projects. While it is true that the Silver-Foster barrage will be shorter and only entomb the Tilbury area, rather than all of Canvey Island and Chatham, the cost for locks will be the same wherever the locks are placed.
But note that the current proposal for a new London barrage is from Sheerness to Southend - in other words exactly where Silver Island is located (hence my suggestion for this location in the first place). And if you are going to build such a huge barrier across the Thames estuary, then why not stick a motorway on top of it, and an airport right beside it? Seems reasonable to me....
Bear in mind, however, that these locks can be left open most of the time. The present barrage only closes about 5 times a year, and I expect the new one will operate similarly.
PAX:
At the risk of sounding like a broken record: No new airport will be built in the South Easth of England in the next 25 years. Reasons have been detailed several times in this thread already. Now, back to the debate.
Then what to do? LHR will wither and die if something is not done. I already avoid the place like a plague because of previous bad experiences. I'll even transit via Madrid, rather than LHR, and I am sure many others feel the same.
And all of this is lost traffic and lost income to UK PLC. If it is easier to have a head office near Schiphol, then that is where the money will go. And the UK will wither and die alongside LHR.
And divided or fractured hubs is not really what is needed. Yes there will always be domestic traffic and cheaper traffic to LGW and STN, but the premium intercontinental traffic wants a large hub with very good ground and air communications into London/Britain/Europe.
That is what LHR is supposed to be providing, but providing very badly. It is a shame that LHR is in such a rotten place; but with no possibility of expansion it will have to close.